With the recent development of information technology devices, an increasing amount of clerical work such as document preparations are being conducted via computers, and users of such devices are increasingly reading text via display terminals such as cathode-ray tube (CRT) displays and liquid crystal displays that display text, images, videos, and so on. These display devices, in general, quickly display digital data and rewrite displayed images, however, they are difficult to carry around. Moreover, since such display devices are light-emitting devices, reading displayed text or viewing displayed images for a long time strains the eyes. Further, those display devices cannot keep images displayed when they are turned off.
Meanwhile, if users desire to distribute or store the text and images as hard copies, the text and images are printed on paper. When users view the text and images that are printed on paper, they view multiply-scattered reflections of the text and images, and hence, the text and images printed on paper provide the users better visibility and less eyestrain compared with those displayed via light-emitting devices. Further, text and images printed on paper or those printed on paper media are lightweight and easy to handle, and therefore can be read in various postures. However, such paper media are likely to be thrown away after use. Although part of used paper media is recycled, recycling is laborious and costly.
As an image display medium that has advantages of both a display terminal and a paper medium, polymer-dispersed liquid crystals, bistable cholesteric liquid crystals, electrochromic elements, and electrophoretic display elements are well-known. These reflection-type image display media have drawn attention in terms of bright display with a memory capability. Especially, a display medium using electrophoretic display elements has an advantage in terms of display quality and power consumption during operation.
Japanese Patent Application Laid-Open (Translation of PCT Application) No. 2002-511607, for example, discloses microcapsules 22 each containing white particles W, red particles R and a suspending fluid 62 colored with cyan. These microcapsules 22 display cyan color when the particles W and R are respectively moved to bottom parts of the microcapsules when appropriate voltages are applied to electrodes 35 and 45. However, since light absorbed by the particles R gives no effect on formation of colors, the capsules 22 may not efficiently display cyan color.